We modified Tor Launcher to highlight the fact that tor generated a warning or error message. A caution / warning icon is added to the "Open Settings" button within the progress dialog. The same icon is also added to the "Copy Tor Log To Clipboard" button within the Network Settings dialog / wizard.

However, the solution is not perfect because the warning about clock skew is sometimes output by tor before Tor Launcher has opened a control port connection (which is how Tor Launcher receives the log messages from tor). I think we will need some advice from the tor developers to find a way to capture all of the log messages.

I would say this is the #1 usability problem in terms of user support mails that arrive to execdir@.

I guess that is not too surprising.
Kathy and I looked at adding support for CLOCK_SKEW events a couple of months ago but then got interrupted with other work. But if I remember correctly, we found that Tor Launcher misses the CLOCK_SKEW event that happens early during tor startup for the same reason Tor Launcher misses other things: it is not connected to the control port yet. That means our best hope at the moment for fixing this problem is #21542 (which would allow Tor Launcher to capture log messages via stderr).

In the user support mails, they are sending us the output of "copy logs to clipboard". Those logs come from events, right?

I think for many of the users, Tor is stuck in a loop where it tries to fetch a directory object, gets upset about its clock and aborts that try, and then does it again a little while later. So even if Tor Launcher misses the first few iterations of that loop, there are plenty more iterations after that.

In the user support mails, they are sending us the output of "copy logs to clipboard". Those logs come from events, right?

I think for many of the users, Tor is stuck in a loop where it tries to fetch a directory object, gets upset about its clock and aborts that try, and then does it again a little while later. So even if Tor Launcher misses the first few iterations of that loop, there are plenty more iterations after that.

About 7 tries in the first 30 seconds, and then it gives up for a while.

FWIW: Firefox has an own mechanism to detect clock skew because of certificate invalidation concerns, see: ​https://bugzilla.mozilla.org/show_bug.cgi?id=1339329. It might be not fine-grained enough for our purposes but I figured I should mention it at least for completeness sake.